Visual motion processing in one-month-old infants: Habituation experiments

The ability of infants to discriminate between opposite directions of motion was examined in infant control habituation experiments. A group of 3-5-week-olds showed no evidence of discrimination between a random-dot pattern which was segregated into regions that moved in opposite directions, and a uniform pattern in which the dots all moved in the same direction. However, they did discriminate between segregated and uniform patterns in two additional conditions, neither of which required sensitivity to direction: in the first of these, segregation was based on the contrast between coherently moving and stationary dots, while in the second the contrast was between coherently and incoherently moving dots. Unlike the younger infants, a slightly older group of 6-8-week-olds proved capable of discriminating between the segregated and uniform patterns when the contrast was between opposite directions of motion. These results confirm and extend the results from preferential looking [Wattam-Bell, J. (1996). Motion processing in one-month-old infants: Preferential looking experiments. Vision Research, 36, 1671-1677]; they suggest that direction discrimination may not emerge until around 6-8 weeks of age. The apparent lack of direction discrimination before 6 weeks may reflect an inability to use directional cues to visually segment the segregated pattern, rather than an insensitivity to direction as such. To examine this, a further set of infants was tested for absolute direction discrimination-i.e., between leftwards- and rightwards-moving uniform patterns. However, in this case neither 3-5- nor 6-8-week-olds showed any evidence of discrimination, which suggests that direction discrimination may first emerge for relative motion. Possible reasons for this are discussed.